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>Appendix F. Additional Supplied Modules</TD
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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AUTO-EXPLAIN"
>F.3. auto_explain</A
></H1
><P
>  The <TT
CLASS="FILENAME"
>auto_explain</TT
> module provides a means for
  logging execution plans of slow statements automatically, without
  having to run <A
HREF="sql-explain.html"
>EXPLAIN</A
>
  by hand.  This is especially helpful for tracking down un-optimized queries
  in large applications.
 </P
><P
>  The module provides no SQL-accessible functions.  To use it, simply
  load it into the server.  You can load it into an individual session:

</P><PRE
CLASS="PROGRAMLISTING"
>LOAD 'auto_explain';</PRE
><P>

  (You must be superuser to do that.)  More typical usage is to preload
  it into all sessions by including <TT
CLASS="LITERAL"
>auto_explain</TT
> in
  <A
HREF="runtime-config-resource.html#GUC-SHARED-PRELOAD-LIBRARIES"
>shared_preload_libraries</A
> in
  <TT
CLASS="FILENAME"
>postgresql.conf</TT
>.  Then you can track unexpectedly slow queries
  no matter when they happen.  Of course there is a price in overhead for
  that.
 </P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN130162"
>F.3.1. Configuration Parameters</A
></H2
><P
>  There are several configuration parameters that control the behavior of
  <TT
CLASS="FILENAME"
>auto_explain</TT
>.  Note that the default behavior is
  to do nothing, so you must set at least
  <TT
CLASS="VARNAME"
>auto_explain.log_min_duration</TT
> if you want any results.
 </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="VARNAME"
>auto_explain.log_min_duration</TT
> (<TT
CLASS="TYPE"
>integer</TT
>)</DT
><DD
><P
>      <TT
CLASS="VARNAME"
>auto_explain.log_min_duration</TT
> is the minimum statement
      execution time, in milliseconds, that will cause the statement's plan to
      be logged. Setting this to zero logs all plans. Minus-one (the default)
      disables logging of plans.  For example, if you set it to
      <TT
CLASS="LITERAL"
>250ms</TT
> then all statements that run 250ms or longer
      will be logged. Only superusers can change this setting.
     </P
></DD
><DT
><TT
CLASS="VARNAME"
>auto_explain.log_analyze</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
>      <TT
CLASS="VARNAME"
>auto_explain.log_analyze</TT
> causes <TT
CLASS="COMMAND"
>EXPLAIN ANALYZE</TT
>
      output, rather than just <TT
CLASS="COMMAND"
>EXPLAIN</TT
> output, to be printed
      when an execution plan is logged. This parameter is off by default.
      Only superusers can change this setting.
     </P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>       When this parameter is on, per-plan-node timing occurs for all
       statements executed, whether or not they run long enough to actually
       get logged.  This can have extremely negative impact on performance.
      </P
></BLOCKQUOTE
></DIV
></DD
><DT
><TT
CLASS="VARNAME"
>auto_explain.log_verbose</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
>      <TT
CLASS="VARNAME"
>auto_explain.log_verbose</TT
> causes <TT
CLASS="COMMAND"
>EXPLAIN VERBOSE</TT
>
      output, rather than just <TT
CLASS="COMMAND"
>EXPLAIN</TT
> output, to be printed
      when an execution plan is logged. This parameter is off by default.
      Only superusers can change this setting.
     </P
></DD
><DT
><TT
CLASS="VARNAME"
>auto_explain.log_buffers</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
>      <TT
CLASS="VARNAME"
>auto_explain.log_buffers</TT
> causes <TT
CLASS="COMMAND"
>EXPLAIN
      (ANALYZE, BUFFERS)</TT
> output, rather than just <TT
CLASS="COMMAND"
>EXPLAIN</TT
>
      output, to be printed when an execution plan is logged. This parameter is
      off by default. Only superusers can change this setting. This
      parameter has no effect unless <TT
CLASS="VARNAME"
>auto_explain.log_analyze</TT
>
      parameter is set.
     </P
></DD
><DT
><TT
CLASS="VARNAME"
>auto_explain.log_format</TT
> (<TT
CLASS="TYPE"
>enum</TT
>)</DT
><DD
><P
>      <TT
CLASS="VARNAME"
>auto_explain.log_format</TT
> selects the
      <TT
CLASS="COMMAND"
>EXPLAIN</TT
> output format to be used.
      The allowed values are <TT
CLASS="LITERAL"
>text</TT
>, <TT
CLASS="LITERAL"
>xml</TT
>,
      <TT
CLASS="LITERAL"
>json</TT
>, and <TT
CLASS="LITERAL"
>yaml</TT
>.  The default is text.
      Only superusers can change this setting.
     </P
></DD
><DT
><TT
CLASS="VARNAME"
>auto_explain.log_nested_statements</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
>      <TT
CLASS="VARNAME"
>auto_explain.log_nested_statements</TT
> causes nested
      statements (statements executed inside a function) to be considered
      for logging.  When it is off, only top-level query plans are logged. This
      parameter is off by default. Only superusers can change this setting.
     </P
></DD
></DL
></DIV
><P
>   In order to set these parameters in your <TT
CLASS="FILENAME"
>postgresql.conf</TT
> file,
   you will need to add <TT
CLASS="LITERAL"
>auto_explain</TT
> to
   <A
HREF="runtime-config-custom.html#GUC-CUSTOM-VARIABLE-CLASSES"
>custom_variable_classes</A
>.  Typical usage might be:
  </P
><PRE
CLASS="PROGRAMLISTING"
># postgresql.conf
shared_preload_libraries = 'auto_explain'

custom_variable_classes = 'auto_explain'
auto_explain.log_min_duration = '3s'</PRE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN130248"
>F.3.2. Example</A
></H2
><PRE
CLASS="PROGRAMLISTING"
>postgres=# LOAD 'auto_explain';
postgres=# SET auto_explain.log_min_duration = 0;
postgres=# SELECT count(*)
           FROM pg_class, pg_index
           WHERE oid = indrelid AND indisunique;</PRE
><P
>   This might produce log output such as:
  </P
><PRE
CLASS="SCREEN"
>LOG:  duration: 3.651 ms  plan:
  Query Text: SELECT count(*)
              FROM pg_class, pg_index
              WHERE oid = indrelid AND indisunique;
  Aggregate  (cost=16.79..16.80 rows=1 width=0) (actual time=3.626..3.627 rows=1 loops=1)
    -&#62;  Hash Join  (cost=4.17..16.55 rows=92 width=0) (actual time=3.349..3.594 rows=92 loops=1)
          Hash Cond: (pg_class.oid = pg_index.indrelid)
          -&#62;  Seq Scan on pg_class  (cost=0.00..9.55 rows=255 width=4) (actual time=0.016..0.140 rows=255 loops=1)
          -&#62;  Hash  (cost=3.02..3.02 rows=92 width=4) (actual time=3.238..3.238 rows=92 loops=1)
                Buckets: 1024  Batches: 1  Memory Usage: 4kB
                -&#62;  Seq Scan on pg_index  (cost=0.00..3.02 rows=92 width=4) (actual time=0.008..3.187 rows=92 loops=1)
                      Filter: indisunique</PRE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN130253"
>F.3.3. Author</A
></H2
><P
>   Takahiro Itagaki <CODE
CLASS="EMAIL"
>&#60;<A
HREF="mailto:itagaki.takahiro@oss.ntt.co.jp"
>itagaki.takahiro@oss.ntt.co.jp</A
>&#62;</CODE
>
  </P
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